Secondary seal for floating roof tanks



29, 1967 A. H. NELSON SECONDARY SEAL FOR FLOATING ROOF TANKS 3 Sheets-Sheet 1 Filed Feb. 24, 1964 .INVENTOR ATTORNEYS Hg eu. NELSON Aug. 29, 1967 H. NELSON SECONDARY SEAL FOR FLOATING ROOF TANKS 3 Sheets-Sheet :3

Filed Feb. 24, 1964 INVENTOR ARM-L NELSON ATTORNEYS Aug. 29. 1967 H. NELSON SECONDARY SEAL FOR FLOATING ROOF TANKS 5 Sheets-Sheet 3 Filed Feb. 24, 1964 INVENTOR ARDGLL N Bid; 6 Q W ATTORNEYj' United States Patent Ofiice 3,338,454 Patented Aug. 29, 1967 3,338,454 SECONDARY SEAL FOR FLOATING ROOF TANKS Ardell H. Nelson, Clarendon, Pa., assignor to Dorcon Incorporated, Warren, Pa., a corporation of Delaware Filed Feb. 24, 1964, Ser. No. 346,638 15 Claims. (Cl. 220-26) This invention relates to seals, and more particularly to seals adapted to be mounted on a floating roof of a tank for storing fluids such as petroleum, so that the fluid within the tank cannot escape between the edge of the roof and the inside surfaces of the tank and various parts of the roof and tank are protected from the elements, from dirt, and from other foreign matter.

One of the continuing problems relating to the storage of petroleum products and other fluids in conventional storage tanks, is the prevention of evaporation losses of the stored product. Conventional storage tanks are provided with a vent in the top or roof thereof. If these conventional tanks were not provided with a vent, then the tanks would collapse or explode in use, due to the vacuum or excessive pressures that would be developed therein. It would not be feasible from an economic standpoint to construct these tanks with suflicient strength to withstand the pressures and vacuum developed therein during use.

When petroleum products and other fluids are stored in ordinary vented tanks, losses of the stored product occur during empty and fill cycles of the tank because when the tank is filled, the vaporized stored product within the tank is expelled through the vent. Losses of the stored product in the tank also occur when the tank is subjected to the normal daily cycle of atmospheric warming and cooling. This is because as the tank warms up during the day, the vaporized stored product in the top of the tank expands and is expelled into the atmosphere through the vent in the top of the tank.

To minimize losses of stored fluids within tanks, the

- floating tank roof was developed. Since the floating roof floats on the stored product within the tank, the stored product is not exposed and the evaporization thereof is substantially eliminated. Thus, the floating roof substantially eliminates the above described losses of products stored within tanks. Two conventional designs of floating roofs are the double-decked type and the pontoon type. Both types serve to insulate the stored product from changes in the surrounding atmospheric temperature, however, the double-deck type is more effective in this respect.

Since the floating room floats on top of the stored product and moves up and down therewith, various types of seals between the floating roof and the tank shell have been devised and used to further minimize evaporation losses of the storedproduct, and at the same time to reduce fire hazards. Typical seal assemblies now in use include a primary seal between the edge of the floating tank and the tank shell and a secondary or weater-seal between the edge of the floating roof and the tank shell above the primary seal. The secondary seal may be exposed to the elements and serve to protect the primary seal. The effectiveness of the primary seal is dependent on the secondary seal. The secondary seal is commonly referred to as a weather-shield.

Primary seals now in use are the metal shoe type, liquid filled tubes, gas filled tubes, and foam filled tubes or variations of the proceeding. Conventional secondary seals currently in use comprise annular rubber or synthetic sheets reinforced with metal ribs, annular foam filled rubber or synthetic sheets, annular extruded rubber sheets, or annular sections of sheet metal or plastic which may or may not be reinforced with ribs. The conventional secondary seals now in use are either partially or completely ineffective. The primary deficiency of conventional secondary seals is that they do not maintain a con tinuous positive contact with the tank shell if the tank is out of round or irregular in cross sectional shape. Most storage tanks are irregular in shape due to fabrication and erection tolerances, and they also get out of round due to settlement of the tank after fabrication. When the secondary seal is not in contact with the inner surface of the tank shell, contaminants such as water or other foreign matter are permitted to enter the tank and thus pollute the stored product, and also the primary seal is exposed to the elements thereby causing it to deteriorate in a relatively short period of time.

It is a primary object of this invention to provide a completely new and novel secondary seal for the floating roofs of storage tanks which overcomes the above mentioned deficiencies of conventional secondary seals.

It is another object of this invention to provide a novel secondary or weather-shield for floating tank roofs which provides complete protection from the elements for the primary roof seal, the connections attaching the primary seal to the floating roof, and the connections attaching the weather-shield itself to the floating roof. This complete protection is provided by the secondary seal regardless of whether the tank is perfectly round or out of round. The secondary seal may be used effectively on tanks that either have an open top or a fixed roof attached to the top of the tank.

, It is another object of the invention to provide a secondary seal for floating tank roofs which is effective to prevent rain, snow, hail, sleet, and wind blown debris such as scale and rust from passing the seal and contaminating the product stored in the tank. The secondary seal also prevents water from running down the side of the tank and contacting the connections which attach the secondary and primary seals to the floating roof.

It is another object of this invention to provide a weather shield for floating roof tanks which is completely effective during periods of very severe icing conditions and which is so designed as to prevent ice or snow accumulating on the weather-shield.

It is yet another object of this invention to provide a novel seal unit for floating roof tanks which is so eflicient that it may function both as a weather-shield and as a primary seal.

It is still another object of this invention to provide a secondary seal unit for floating roof tanks which will effectively conduct electrical charges built up on the roof to the side walls of the tank, is economical to manufacture, is durable and reliable in use, is attractive in appearance, is continuous and flexible so as to maintain sealing contact around the entire periphery of the tank shell even through it may be out of round, will not damage the protective coating on the inner surface of the tank with which it is used,.may be used with any size tank, and may be easily inspected while in service.

Yet another object of this invention is to provide a novel seal unit for floating tank roofs which cannot flip over backwards since it is always maintained in sealing contact with the surface of the tank on which it is used by its own weight or by resilient means.

An advantage of the seal comprising this invention over conventional seals is that it permits the tank on which it is used to be utilized to its full capacity without requiring an extension, and it has a smooth sloping exposed surface so as to shed rain, ice, snow, etc.

The invention will be best understood from a consideration of the following detailed description taken in connection with the accompanying drawings, wherein:

FIG. 1 -is a vertical cross sectional view taken through a storage tank having a pontoon-type floating roof which is sealed from the inner surfaces of the tank by a primary seal and the secondary seal of this invention;

FIG. 2 is a view similar to FIG. 1, but showing a double deck-type floating roof;

FIG. 3 is a reduced plan view of FIG. 1;

FIG. 4 is an enlarged view of a portion of FIG. 3 with portions broken away;

FIG. 5 is a plan view similar to FIG. 3 but showing the invention used with a non-circular tank;

FIG. 6 is a plan view similar to FIG. 3 showing the roof in non-concentric relation to the tank; I

FIG. 7 is an enlarged vertical cross sectional view taken substantially on the plane of line 77 of FIG. 4;

FIG. 8 is a vertical cross sectional view similar to FIG. 7 but showing a modified form of the invention;

FIG. 9 is a vertical cross sectional view of another form of the invention;

FIG. 10 is an enlarged view of the encircled portion of FIG. 9.

FIG. 1 illustrates in vertical cross section a conventional storage tank 10 having an open top and comprising cylindrical or substantially cylindrical side walls 12 connected at their bottom edges to a circular floor 14. Tank 10 is of the type used for storing. fluids such as a petroleum product 16. A floating roof 18 floats on the fluid 16 and prevents evaporation thereof. Roof 18 is of the pontoon type and includes an annular hollow pontoon 20. Pontoon 20 is substantially rectangular in cross section and comprises concentric circular vertical walls 22 and 24 sealingly connected together by a circular bottom wall 26 and a circular upper wall 28 so as to define an annular gas filled chamber 30. The circular opening defined by the wall 24 is closed by a horizontal partition 32 secured to wall 24. The upper wall 28 slopes inwardly towards the partition 32 so as to deflect rain, snow, dirt and other foreign matter away from the peripheral edges of the floating roof.

An annular primary seal 34 is provided between the outer surface of the roof 18 and the inner surface of the tank 10 so as to prevent escape or evaporation of the fluid 16 between the roof and the tank. A secondary seal or weather-shield 36 of novel construction is secured to the upper edge of roof 18 above the primary seal so as to extend across the gap between the roof and tank and prevent exposure of the primary seal to the elements as well as to prevent foreign material such as dirt, water, snow, etc., from contacting the primary seal and the connections securing the primary seal and the secondary seal to the floating roof 18.

The storage tank 10' shown partially in FIG. 2 is of substantially the same design as the storage tank 10 except it is provided with a double-deck type floating roof 38. Roof 38 includes a circular bottom wall 26' and a conical upper wall 28 connected together at their edges by an annular outer wall 22' so as to define a substantially circular gas filled chamber 30. The central portion of the roof is reinforced by a cylindrical inner wall 24 which extends between and is secured to the bottom wall 26' and the upper wall 28'. The double deck roof 38 more effectively insulates the fluid 16 from exterior heat than the pontoon type roof 18 because of its larger gas filled chamber 30. The more effective insulation since it reduces heating of the fluid 16, substantially reduces evaporation of the fluid which could pass between the seals and tank surfaces in the form of a gas.

The roof 38 is also provided with primary and secondary seals 34 and 36 in the same manner as the roof 18.

Primary seals now in use are the metal shoe type, liquid filled tubes, gas filled tubes, and foam filled tubes, or variations of the proceeding. The details of a suitable form of a primary seal 34 is illustrated in FIG. 7. The primary seal is located Within the annular space 40 provided between the inner surface of the tank wall 12 and the outer peripheral surface of the outer wall 22 of the floating roof.

Seal 34 includes an annular hollow, endless tube 42 prefer ably formed of fluid impervious and flexible material. The upper edge of the outer wall 22 terminates in an inwardly extending annular flange 44. A plurality of vertically extending support plates are circumferentially spaced around the outer peripheral surface of the circular wall 22. The upper edge of each support plate 46 is integrally connected to a flange 48 which extends over the flange 44. An annular pipe member 50 extends around the wall 22 and is secured to the lower ends of each of the support plates 46. An annular sheet of material 52 is folded around the members 48, 46, 5t and 42, so as to completely enclose these members and contain them within an annular space 54. The circular edges of sheet 52 are substantially aligned with one another and with the free edges of the flanges 48. Preferably, the material 52 is waterproof or liquid impervious and has a very low coefficient of friction so as to easily slide upon the inner surface of the tank wall 12. The tube 42 is preferably filled with liquid, gas, or foam material so as to cause it to expand and thereby urge opposite sides of the sheet 52 into sealing engagement with wall 12 and wall 22.

Secondary seals currently in use vary from almost complete ineffectiveness to limited effectiveness. The main problems associated with conventional secondary seals are that they do not maintain a continuous positive contact with the tank shell, particularly if the tank is out of round or irregular as often occurs due to fabrication tolerances and settlement of the tank. The novel secondary seal 36 shown in detail in FIGS. 4 and 7 overcomes the deficiencies of conventional secondary seals.

The secondary seal or Weather-shield 36 includes an annular clamping ring 56 supported on the upper edge of the sheet 52. A plurality of flexible ribs are circumferentially spaced around the ring 56 and secured thereto. Each rib 58 includes a central body portion 60 which extends upwardly and radially outwardly at an angle of substantially 45 to 60 to the horizon. The lower end of each body portion 60 is integrally secured to a horizontal flange 62 wihch overlies the ring 56. The upper end of each rib is bent into a substantially oval-shaped loop 64 integrally secured to the upper end of the bordy portion 60. Each loop 64 incloses a vertically elongated space 66. The up per end of each loop 64 includes a flange or cam portion 68 which slopes upwardly and inwardly relative to the tank wall 12 and a bottom flange 70 which extends substantially perpendicular to the wall 12. The sides of the loop 64 are substantially parallel to one another and to the wall 12.

An annular sheet of material 72 has one of its edges clamped between the flange 44 and the lower edge portion of the sheet 52. The sheet 72 extends upwardly over the inner edge of the ring 54 and then slopes upwardly and radially outwardly to the top of the loop 64. The sheet 72 is then folded over the upper edges of the ribs 58 so as to extend over the cams 68 and pass downwardly between the loops 64 and the inner surface of the wall 12. The upper edge portion of the sheet 72 is folded down along the underside of each rib body 60 and secured thereto by nut and bolt assemblies 74. The upper edge of the sheet 72 is curved downwardly from the nut and bolt assembly 74 and the ribs 58 so as to form a vertically extending drip edge 76.

The various components of the seals are secured to the floating roof by conventional means such as a bolt 78 extending through the edges of sheets 52 and 72, ring 56, members 44 and 48 and flange 62. A nut 80 is threaded on the bolt 7 8 so as to clamp the seal members together and secure them to the floating roof.

Like the sheet 52, the sheet '72 is composed preferably of a waterproof material that has a very low coefiicient of friction such as certain types of sheet metal or sheet plastic as nylon. If desired, the sheets 52 and 72 may be integrally secured together adjacent the flange 44 so as to form one continuous integral piece. The ribs 58 are preferably composed of resilient metal which urge the vertical portion 82 of sheet 72 snugly into engagement with the inner surface of wall 12.

A thin, flexible, continuous, endless and resilient metal ring 84 passes through all the oval spaces 66 of loops 64, and since this ring is only slightly smaller in diameter than the inside diameter of the tank wall 12, the ring urges the sheet portion 82 radially outwardly into snug sealing engagement with the wall 12.

As shown in FIG. 4, the ribs 58 are preferably equally spaced in a circumferential direction around the periphery of the floating roof, and preferably spaced the same as and located directly above the supporting plates 46. The ring 84 is free to move in a circumferential direction through and relative to the loops 64. It is the action of the ring 84 which assures that the secondary seal 36 provides a positive and completely effective seal between the floating roof and the tank 12 regardless of the irregularities and out of roundness of the tank wall. The ring 84 continuously urges the sheet portion 82 into engagement with the tank wall 12 regardless of the cross sectional shape of the tank wall. The ribs 58 may also resiliently urge ring 84 and portion 82 radially outwardly to provide a more effective seal. FIG. 4 illustrates how the ring 84 maintains the secondary seal 36 in sn-ug engagement with a circular tank wall 12. FIG. 5 illustrates how the ring 84 maintains the secondary seal 36 in continuous engagement throughout its periphery with the inner surface of a tank wall 12' which is out of round. Since the ring 84 is flexible and resilient, it automatically follows the contours of the tank wall so as to force the seal 36 snugly into engagement therewith. Since the ring 84 is freely slidable in a circumferential direction relative to the ribs 58, it readily moves relative to the ribs to form fit a non-circular tank. FIG. 6 illustrates how the flexible ring 84 forces the secondary seal 36 to sealingly engage throughout its periphery the inner surface of a tank 12" even though the floating roof and tank wall may be eccentric relative to each other. However, the flexible ring 84 will tend to maintain the floating roof in concentric relation relative to the tank.

The secondary seal 36 illustrated in FIG. 8 is identical to the secondary seal 36 in FIG. 7 except additional parts have been added thereto, and like parts have been given the same reference numerals. The primary seal 34 is also identical to that shown in FIG. 7. The seal 36 includes a ring of flexible material preferably of thesame composition as the material comprising the sheet 72. The ring 86 is concave or substantially U-shaped in cross section and has opposite edges secured to the upper portion of sheet 72 by conventional means such as glueing or bonding. The central portion of the ring 86 is spaced radially outwardly from the portion 82 of sheet 72 so as to provide an annular space which is preferably filled with a resilient material such as foam rubber 88. The foam material 88 effectively urges the central portion of the ring 86 radially outwardly thereby causing it to more effectively follow any depressions or irregular surfaces on the wall 12.

In use, the primary seal 34 effectively seals the space 10 between the floating roof and the tank wall 12 so as to prevent evaporation of the fluid 16 and prevent vapors from'passing above the floating roof which would not only result in a fire hazard, but also over a period of time result in a substantial wastage of the stored product. Any vapors that may pass the primary seal 34 are prevented from escaping by the secondary seal 36 or 36'. The seal 36' also functions as a weather-shield and prevents ice, snow, water, dirt and other debris from passing into the space 40' between the primary and secondary seals. Any foreign material contacting the secondary seal is deflected downwardly onto the floating roof by means of the exposed sloping surface of the sheet 72. Any water or other substance that may pass between the secondary seal and the wall 12 flows downwardly onto the drip edge 76 and is thereby prevented from reaching the connections at the bolts 78. This is quite important, because if water or other substances were allowed to flow from the edge 76 to the ribs 58, the bolts 78, nuts 80 and ring 56 would be corroded and damaged. The seal 36 also protects the primary seal 34 from the elements thereby substantially increasing the life and effectiveness of the primary seal.

The weight of the secondary seal assists in maintaining it in contact with the wall 12, and this Weight in conjunction with the ring 84 prevents the secondary seal from separating from the wall 12. The material comprising sheet 72 may be coated with or contain substancesso that any static electricity on the floating roof may be conducted safely to the wall 12 of the tank. Since the material comprising the sheets 75 and 52 have a low co efficient of friction, the seals may slide easily on the inner surfaces of the wall 12 Without damaging the protective coating on the wall.

Since the seal unit 36 is Very durable and provides a highly efiicient seal, it may be used without the primary seal 34, particularly on tanks. which are provided with a permanent fixed roof as illustrated in FIGS. 9 and 10 wherein a seal unit 11 is illustrated as being used on a floating pontoon type roof 18' within a tank 10" having a fixed roof attached to the upper edge of the tank in spaced relationship thereto by vertical support members 92. The seal 36" shown in FIGS. 9 and 10 is substantially the same as the seal 36 in FIG. 7, and like parts are indicated by the same reference numerals. However,

since the seal 34 has been omitted, bolt 78' which secures the seal 36" to the floating roof may be substantially shorter than the bolt 7 8 in FIG. 7. The seal 36" functions as both a weather-shield and a primary seal. The space above the floating roof 18' is vented by means of the' clearance between the roof 90 and the upper edge of tank 10".

The various seals shown in FIGS. 7, 8 and 10, may be used with both the pontoon roof 18 shown in FIG. 1, and the double deck roof 38 shown in FIG. 2. as well as with other types of roofs.

Inasmuch as various changes may be made in the form, location and relative arrangement of the several parts without departing from the essential characteristics of the invention, it'will be understood that the invention is not to be limited except by the scope of the appended claims.'

I claim:

1. A seal for sealing the space between the edge of a floatingroof and the shell of a storage tank comprising: sealing means adapted to sealingly and slidably engage an inner surface of the shell, flexible means adjacent said sealing means urging said sealing means away from the roof towards said inner surface so that said sealing means will maintain continuous sealing contact with said surface when there is relative movement between the roof and shell, and mounting means for mounting said sealing means and flexible means on said roof so that said sealing means and flexible means may move relative to said roof and said sealing means will remain in sealing contact with said surface regardless of irregularities in its shape, said flexible means comprising a resilient ring of metal having a radial dimension that is small relative to its vertical dimension, and said mounting means for said resilient ring comprising a plurality of circumferentially spaced flexible ribs each having an outer and an inner end, the inner" neans includes an annular sheet of material above said 'ibs and extending from the inner ends of said ribs to he outer ends thereof, said sheet of material having a 'adia'lly outer edge portion of annular shape folded over ;he outer ends of said ribs and said ring so as to be forced radially outwardly by said ring in continuous seal- .ng engagement with said inner surface of said shell.

4. A storage tank including a substantially cylindrical- ;h-aped vertically extending shell, a substantially circular floating roof extending horizontally within said shell and of smaller diameter than said shell, a seal unit comprising a flexible ring member within said shell, a substantially annular flexible seal means between said ring member and said shell, said ring member urging said seal means into sealing engagement wit-h said shell throughout its periphery, and flexible means mounting said ring member on said floating roof so that said ring member may move freely in a circumferential and radial direction relative to said floating roof and oircumferentially slidable relative to said mounting means said seal unit effectively seals the space between said floating roof and said shell, and said ring member being composed of sheet metal and having a radial dimension that is thin in relation to its vertical dimension.

5. A storage tank as defined in claim 4, wherein said mounting means includes a plurality of upwardly and radially outwardly extending flexible arms spaced circumferentially about and connected to an edge of said floating roof.

6. A storage tank as defined in claim 4, wherein said floating roof is of the pontoon type.

7. A storage tank as defined in claim 4, wherein said floating roof is of the double deck type.

8. A storage tank as defined in claim 4, including a primary seal of annular shape mounted on said floating roof below said seal unit and in the space between said floating roof and the shell.

9. A storage tank as defined in claim 5, wherein said sealing means includes a sheet of material having a low coefficient of friction and two edge portions, one edge portion of said sheet being clamped between said arms and said edge of said roof, said sheet extending over said arms and ring means and downwardly between said ring means and the inner surface of said shell, and means securing the outer edge portion of said sheet in operative position.

10. A storage tank as defined in claim 9, wherein said other edge portion includes a free edge extending downwardly away from said arms so as to define a drip edge which prevents any liquid moving downwardly past said ring member from contacting said arms.

' 11. A storage tank as defined in claim 9, wherein said seal element includes a hollow annular flexible member filled with resilient foam material engaging said shell throughout its periphery and supported on said arms.

12. A storage tank as defined in claim 9, including a primary seal below said seal unit and within the space between said floating roof and said shell, said primary seal including an annular flexible tube, a vertically extending support member below each of said arms and having an upper end extending under the inner end of one of said arms, a second sheet of material folded over said tube and support means so that the edges of said second sheet lie over opposite sides of the upper ends of said support members, an elongated securing means extending through the upper edge of said roof, the inner end of 8 each arm, the upper end of each support member and the edges of said second sheet so as to secure them together.

13. A storage tank as defined in claim 10, wherein said arms each are inclined upwardly and radially outward-1y from the upper edge of said floating roof, each arm having a substantially horizontal inner end secured to said upper edge of said roof and an upper end formed into a vertically elongated loo each loop freely and slidably receiving a portion of said ring means.

14. A storage tank as defined in claim 12, including an annular clamping ring between the inner ends of said arms ad an edge of said second sheet.

15. A storage tank including a substantially cylindricalshaped vertically extending shell, a substantially circular floating roof extending horizontally within said shell and of smaller diameter than said shell, a dual seal unit positioned about the periphery of said roof, comprising lower and upper spaced ring seals defining primary and secondary seals, a clamping ring therebetween securing said seals to the periphery of the floating roof, support means for said seals extending from said clamping ring, a flexible ring carrying said secondary seal; said support means for said secondary seal comprising a plurality of upwardly and radially outwardly extending flexible arms arranged in circumferentia-lly spaced relation about and having their lower ends secured to said clam-ping ring and their upper ends secured to said flexible ring in circumferentially slidable relation thereto; said support means for said lower seal comprising spaced downwardly extending plates which are secured at their upper ends to said clam-ping ring; means securing the lower ends of said plates together; sheet material positioned over said clamping ring, said arms, and said flexible ring of said upper seal and secured thereto; and sheet material completely enclosing said downwardly extending plates and said means for securing their lower ends together and having its edges secured to said clamping ring and forming an annular looped enclosure; said enclosure having an expandable endless tube therein and forming therewith said lower seal; and means clamping said clamping ring, said arms, said plates and said sheets to the top edge of said floating roof, whereby said secondary seal contacts said shell above the plane of the top peripheral edge of the floating roof and said primary seal contacts said shell below said plane of said edge.

References Cited UNITED STATES PATENTS 1,698,158 1/1929 Glass 220--26 2,057,682 10/ 1936 Horton et al 22026 2,089,645 8/ 1937 Dickmann 220 -26 2,516,101 7/1950 Boberg 22026 2,531,424 11/1950 Goldsby et al 220--26 3,043,468 7/ 196-2 Harner 22026 3,054,526 9/ 1962 Mercier 220 -26 3,185,335 5/1965 Lecler 220-26 3,204,808 9/1965 Cadwell 22026 3,204,809 9/ 1965 Cadwell 22026 FOREIGN PATENTS 92,546 5/ 1922 Switzerland.

THERON E. CONDON, Primary Examiner. JAMES R. GARRETT, Examiner. 

15. A STORAGE TANK INCLUDING A SUBSTANTIALLY CYLINDRICALSHAPED VERTICALLY EXTENDING SHELL, A SUBSTANTIALLY CIRCULAR FLOATING ROOF EXTENDING HORIZONTALLY WITHIN SAID SHELL AND OF SMALLER DIAMETER THAN SAID SHELL, A DUAL SEAL UNIT POSITIONED ABOUT THE PERIPHERY OF SAID ROOF, COMPRISING LOWER AND UPPER SPACED RING SEALS DEFINING PRIMARY AND SECONDARY SEALS, A CLMAPING RING THEREBETWEEN SECURING SAID SEALS TO THE PERIPHERY OF THE FLOATING ROOF, SUPPORT MEANS FOR SAID SEALS EXTENDING FROM SAID CLAMPING RING, A FLEXIBLE RING CARRYING SAID SECONDARY SEAL; SAID SUPPORT MEANS FOR SAID SECONDARY SEAL COMPRISING A PLURALITY OF UPWARDLY AND RADIALLY OUTWARSLY EXTENDING FLEXIBLE ARMS ARRANGED IN CIRCUMFERENTIALLY SPACED RELATION ABOUT AND HAVING THEIR LOWER ENDS SECURED TO SAID CLAMPING RING AND THEIR UPPER ENDS SECURED TO SAID FLEXIBLE RING IN CIRCUMFERENTIALLY SLIDABLE RELATION THERETO; SAID SUPPORT MEANS FOR SAID LOWER SEAL COMPRISING SPACED DOWNWARDLY EXTENDING PLATES WHICH ARE SECURED AT THEIR UPPER ENDS TO SAID CLAMPING RING; MEANS SECURING THE LOWER ENDS OF SAID PLATES TOGETHER; SHEET MATERIAL POSITIONTED OVER SAID CLAMPING RING, SAID ARMS, AND SAID FLEXIBLE RING OF SAID UPPER SEAL AND SECURED THERETO; AND SHEET MATERIAL COMPLETELY ENCLOSING SAID DOWNWARDLY EXTENDING PLATES AND SAID MEANS FOR SECURING THEIR LOWER ENDS TOGETHER AND HAVING ITS EDGES SECURED TO SAID CLAMPING RING AND FORMING AN ANNULAR LOOPED ENCLOSURE; SAID ENCLOSURE HAVING AN EXPANDABLE ENDLESS TUBE THEREIN AND FORMING THEREWITH SAID LOWER SEAL; AND MEANS CLAMPING SAID CLAMPING RING, SAID ARMS, SAID PLATES AND SAID SHEETS TO THE TOP EDGE OF SAID FLOATING ROOF, WHEREBY SAID SECONDARY SEAL CONTACTS SAID SHELL ABOVE THE PLANE OF THE TOP PERIPHERAL EDGE OF THE FLOATING ROOF AND SAID PRIMARY SEAL CONTACTS SAID SHELL BELOW SAID PLANE OF SAID EDGE. 